Fastener supports for facilitating the installation of screws and other fasteners are known in various embodiments. One example is shown in U.S. Pat. No. 5,341,708, where the head of a screw is inserted into an apparatus from the free, open end thereof, and is captured by ball-like centering and locking elements in a passageway that are pressed outwards in response to the passage of the screw head. A displaceable sleeve on the apparatus must first be slid or pushed back and held so that the centering and locking elements can move into a position in which they do not engage or block the passageway. Once the sleeve is released, however, the centering and locking elements are forced radially inward and thereby rigidly held. This results in the screw being captively held against the screwing device while the threaded portion of the screw, including the tip, protrudes beyond the apparatus. Such an arrangement might be sufficient for hand-held screwing devices having a slidable chuck-like sleeve. In the case of heavier screwing devices, however, which screwing is to be carried out, for example, in the ground region, it is preferable if the screw does not have to be introduced from below. It is also preferable if the thread or tip of the screw only protrudes from the passageway during the screwing-in process, and not before.
It is also known to feed or deliver screws through a tube or a conduit, which is offset laterally in relation to the screw axis, wherein, at the free or open end of the device placeable on the workpiece in the region of the tubular passage, centering or holding elements for the inserted screws are provided. With such an arrangement, however, once the feeding tube has been swiveled or pivoted into alignment with the screwing-in axis, the tips of the screws and the threaded front regions protrude beyond the apparatus and can thus damage the surface of the workpiece. Such a known construction, as described in DE-A-38 08 889, is more suitable for shorter screws. In the case of longer screws, however, and as a result of the swiveled-out position of the screw holder, problems would be encountered by the interference of the exposed screw with various parts of the device. A further known embodiment, as described in DE-A-31 12 520, provides for the capture of screws supplied by a pivotable screw holder and a passage that is closed off at the bottom in the swiveled-out position. However, as soon as the screw holder has been swiveled into a position in alignment with the screwing-in axis, the screw falls down into the adjoining passage below and the screw shaft is no longer being guided. Such an arrangement is again only practical with very short screws.
Another prior art apparatus for screwing-in screws is shown in EP-A-547638, which consists of a drive shaft having an engaging tool disposed at the freely protruding end thereof and a screw holder with a tubular passage. Axially-separated holding and centering elements for an inserted screw capable of moving outwards engage in two sections of the passage. This apparatus eliminates the above-described disadvantage of the protruding screw. However, for the following reasons, it is also suitable only for relatively short screws. This known apparatus provides two embodiments. In one embodiment, a screw is held simultaneously through both sections by outwardly pivotable locking and centering elements. There must be a relatively narrow axial gap between the holding and centering elements, because a lower element controls an upper element via a projection in such a way that the upper element is always slightly open. Thus, a screw, falling from the top to the bottom, falls past the upper element or clamping jaw without being held thereby, until its tip is held by the clamping site of the lower element or jaw, resulting in the screw being aligned in the apparatus only at its tip. Leaf springs are used to exert pressure on the elements or jaws in their closed position. Obviously, as a result of the short segment on which the shaft of the screw is clamped, only relatively short screws can be centered reliably. In another embodiment, the lower region has a widened inner opening in which two locking jaws are pivotably mounted, which are forced into the closed position by springs. The inner walls of the locking jaws are funnel-shaped, the funnel becoming narrower in the downward direction with an axially aligned opening present in the region of the underside. A descending screw reaches this opening and is therefore automatically centered. A screw falling downwards from the top is thus held between the two locking jaws with its tip through the opening. The upper end of the screw is held by the inner walls of the tube surrounding the head. Any further possible deviation of the longitudinal axis of the screw from the longitudinal axis of the screwing apparatus is governed by the differences in the diameter of the inner opening of the tube and the diameter of the screw head. In order to ensure adequate gripping, even for small screw heads, provisions are made for the insertion of a further tubular element. Obviously, this embodiment of the known screwing apparatus is also suitable only for relatively short screws, since the internal diameter of the tube must essentially be as large as the diameter of the screw head or be reduced in size to the diameter of the screw head by the insertion of an additional tubular element or sleeve. Thus, in this embodiment, screws supplied obliquely from a magazine can reach the tube only if they are very short, because the tube, as described above, can have an internal diameter only of the order of magnitude of the diameter of the screw head, so that the screw can be guided adequately at its upper end. With this embodiment of the known screwing apparatus also, long screws can consequently not be handled and delivered.
This disadvantage is also exhibited in GB 2 206 828 A, wherein axially and angularly spaced locking and centering elements consist of flexible lamellae and protrude inwards towards the tool or screw axis. Four sets of lamellae grip the screw shaft only in the vicinity of the screw tip, while the remaining portion of the screw shaft is gripped only by three sets of lamellae, and the screw must be introduced obliquely laterally through an opening. Obviously, the lateral insertion opening provided and the fact that the inserted screw is only held in the region of its tip only permit relatively short screws to be reliably centered, not to mention the susceptibility of the flexible lamellae to defects and wear, which can greatly impair the centering of even short screws after a brief period of use.